Here are your tips for completing this quest:
- Don't equip a shield in your shield slot, you wont be able to remove it, it doesn't work at all, and it blocks your screen.
- Shield needs to be in your primary hand.
- Arrows deflected must damage a Skeleton to count.
- Right-click once, no need to hold it. You will deflect arrows.
- Have an anvil and iron handy to repair shield (and armor, for those arrows that get thru).
- Dig a trap for the Skeletons that is 2 blocks below you, so skeleton's heads are basically at your waist. They shoot slightly up at you.
- Stand right next to them as close as possible so arrows deflect down at them. If you angle shield up a bit I find more arrows hit them.